This invention relates to a method of completing a well in a poorly consolidated formation-bearing hydrocarbon to minimize flow of particulates such as sand into a wellbore. The invention proposes a screen-less completion method that can be carried out with coiled tubing equipments.
Hydrocarbons (oil, natural gas, etc.) are obtained from a subterranean geologic formation (i.e., a xe2x80x9creservoirxe2x80x9d) by drilling a well that penetrates the hydrocarbon-bearing formation. This provides a partial flowpath for the hydrocarbon to reach the surface. In order for the hydrocarbon to be xe2x80x9cproduced,xe2x80x9d that is travel from the formation to the wellbore (and ultimately to the surface), there must be a sufficiently unimpeded flowpath from the formation to the wellbore. This flowpath is through the formation rockxe2x80x94e.g., sandstone, carbonatesxe2x80x94which has pores of sufficient size, connectivity, and number to provide a conduit for the hydrocarbon to move through the formation.
When hydrocarbon is produced from a well, formation particulates may travel with the hydrocarbon from the formation, through the wellbore, to the surface. The presence of formation particulates is especially likely in soft formations comprising sand, sandstone, chalk, or limestone. The travel of particulates with the hydrocarbon is undesirable. Particulates flowing through the wellbore will erode equipment in the wellbore and at the surface, which can make replacement of such equipment necessary. Particulates in the produced hydrocarbon must also be removed before the hydrocarbon can be processed. Also, particulates can come to reside in the wellbore to the point where hydrocarbon production is greatly diminished or completely stopped.
When faced with formations requiring sand management, the choice is typically between the use of sand exclusion devicesxe2x80x94that usually include a screen and gravelxe2x80x94or screenless completion technologies.
In the conventional sand-control techniques, typically a screen is placed inside the wellbore casing. Gravel is then packed between the screen and the casing. Gravel packs can also be used open-hole (i.e. in wellbores without a casing), or screens can be used without gravel packs. Placing gravel above the fracture pressure of the formation may be termed a xe2x80x9cfrac-pack.xe2x80x9d As hydrocarbons are produced from the formation, they travel through the gravel pack and/or the screen before entering the wellbore. The gravel pack and/or screen inhibit the flow of particulates but, under normal conditions, do not substantially inhibit the production of hydrocarbons. Where the internal diameter of the casing is too small, tubing screen assemblies run on coiled tubing may be applied. However, placing a gravel pack and screen requires specialized equipment and access for electric lines that are not always available, especially with offshore wells. Further, the screen and the gravel pack create a mechanical restriction, may be plugged by scales or eroded by the flow of sand, thereby requiring later expensive re-completions.
Screen-less completions involve consolidating the formation by injecting a consolidating fluid comprising, for example, a resin. They offer the advantage of full bore access, lower skins, and reduce the risk associated with running screens into the wellbore. The economic and logistical advantages associated with screen-less completions have made this approach very desirable.
Conventional consolidating fluids comprise a resin, and optionally a curing agent, a catalyst, and an oil wetting agent. When injected into the formation, the resin (acted upon by the curing agent and catalyst, if present) hardens, causing consolidation of the formation to a rigid state and reduction in the concentration of formation particulates. Consolidating fluids and methods for their use are reported in U.S. Pat. Nos. 5,806,593; 5,199,492; 4,669,543; 4,427,069; and 4,291,766. In practice, resins have been used for many years and are effective for short intervals but are recognized to reduce the permeability of the formation, as discussed by Parlar in SPE 39435. Also resin-coated sands have been used both to repair gravel packs and also to provide sand control in the borehole and perforation tunnel. Combinations of sand and resins have also been used as well as fracture treatments to reduce the drawdown and provide sand control in the formation. (SPE 30467)
International Patent Application 02/04784 teaches the use of flexible gel to consolidate a formation. The consolidating fluid includes a gel component and a gel-forming agent and is injected into the formation under conditions under conditions wherein the consolidating fluid forms a flexible gel, thereby consolidating the formation. According to some embodiments, the consolidated formation is further perforated or fractured.
From U.K. Patent Application No. 2,352,259, it is further known a process for stimulating a hydrocarbon-bearing formation comprising the step of determining the direction of maximum in-situ stress within the formation, perforating the formation in a single vertical plane extending in this direction of maximum stress and performing a propped fracturing treatment with a low viscosity fluid. This technology minimizes the undesirable effect of so-called xe2x80x9cnear-wellbore tortuosityxe2x80x9d and may also be used to minimize productions in weak formations. However, the step of determining the direction of maximum stress requires the use of specific tools, such as an ultrasonic imaging tool, that are not always available especially in some remote locations. Moreover, depending on the type of formations, the interpretation of the logs may be extremely difficult so that there is no practical way of determining the direction of maximum in-situ stress with a good accuracy.
Though screen-less completions are clearly desirable, in practice numeral failures have been reported. Therefore the present invention aims at providing a method of completing a non-completed cased interval in an unconsolidated formation, in particular where the direction of in-situ maximum stress is unknown.
In one embodiment, the present invention relates to a method of completing an interval of a cased well drilled through incompetent formation comprising a combination of three successive operations: zero-degree phasing perforation of a relatively small portion of the interval to be completed, consolidation of the formation zone around the perforations and injection of a propped fracturing fluid above fracture pressure to create a hydraulic fracture and pack this gap with a proppant held by a proppant flowback-retention agent.
The method according to the invention may be carried out with coiled tubing equipment, therefore offering significant cost savings over conventional completions using a rig and screens as well as providing the opportunity to return to other zones either above or below the producing interval and perform additional rig-less completions without screens. Further the method provides an effective way of completing wells in unconsolidated formations even when the horizontal stress direction is not known.